The negative environmental impact of fossil fuels and their rising cost have resulted in a dire need for cleaner, cheaper alternative energy sources. Among different forms of alternative energy sources, solar power has been favored for its cleanness and wide availability.
A solar cell converts light into electricity using the photovoltaic effect. There are several basic solar cell structures, including a single p-n junction, p-i-n/n-i-p, and multi-junction. A typical single p-n junction structure includes a p-type doped layer and an n-type doped layer. Solar cells with a single p-n junction can be homojunction solar cells or heterojunction solar cells. If both the p-doped and n-doped layers are made of similar materials (materials with equal band gaps), the solar cell is called a homojunction solar cell. In contrast, a heterojunction solar cell includes at least two layers of materials of different bandgaps. A p-i-n/n-i-p structure includes a p-type doped layer, an n-type doped layer, and an intrinsic (undoped) semiconductor layer (the i-layer) sandwiched between the p-layer and the n-layer. A multi junction structure includes multiple single junction structures of different bandgaps stacked on top of one another.
In a solar cell, light is absorbed near the p-n junction generating carriers. The carriers diffuse into the p-n junction and are separated by the built-in electric field, thus producing an electrical current across the device and external circuitry. An important metric in determining a solar cell's quality is its energy-conversion efficiency, which is defined as the ratio between power converted (from absorbed light to electrical energy) and power collected when the solar cell is connected to an electrical circuit. High efficiency solar cells are essential in reducing cost to produce solar energies.
In practice, multiple individual solar cells are interconnected, assembled, and packaged together to form a solar panel, which can be mounted onto a supporting structure. Multiple solar panels can then be linked together to form a solar system that generates solar power. Depending on its scale, such a solar system can be a residential roof-top system, a commercial roof-top system, or a ground-mount utility-scale system. Note that, in such systems, in addition to the energy conversion efficiency of each individual cell, the ways cells are electrically interconnected within a solar panel also determine the total amount of energy that can be extracted from each panel. Due to the serial internal resistance resulting from the inter-cell connections, an external load can only extract a limited percentage of the total power generated by a solar panel.
Continuous strings of solar cells that form a solar panel exist. Each string includes several solar cells that overlap one another. This overlapping technique is referred to as “shingling.” U.S. patent application Ser. No. 14/510,008, filed Oct. 8, 2014 and entitled “Module Fabrication of Solar Cells with Low Resistivity Electrodes,” describes several technical advantages that result from shingled cells.
Manufacturing a shingled panel can involve connecting two solar cells by overlapping the cells so that the metal layers on each side of the overlapped cells establish an electrical connection. This process is repeated for a number of successive cells until one string of shingled cells is created. A number of strings are then connected to each other and placed in a frame. One form of shingled panel, as described in the above-noted patent application, includes a series of solar cell strips created by dividing solar cells into smaller pieces (i.e. the strips). These smaller strips are then shingled to form a string.
One problem that arises in manufacturing such shingled panels is that the assembly of shingled strings of solar cells requires precise alignment of the cells to ensure proper electrical connection. Given the level of precision needed to create a shingled string, it is not feasible to manufacture such solar panels in volume manually.